In the thermal imprinting of substrates a carrier with a transfer layer is brought into contact with an object, i.e. substrate, which is to be imprinted. Simultaneously with the contact of the carrier transfer layer with the surface of the object that is to be imprinted, a heated die, i.e. printhead, is brought into engagement with the reverse side of the carrier. This brings about the release of the transfer layer from the carrier to the surface to be imprinted. When the carrier is withdrawn the released transfer layer remains on the object and the imprinting is thus completed.
Thermal imprints are commonly made using heat transfer films which are known as "hot stamp foils", or "roll leaves". The foil or leaf is typically a thin polypropylene or polyester film which is coated with a suitable transfer layer. The result is a laminate made up of the carrier and various layers of the transfer material.
Conventional transfer laminates typically employ at least three functional coatings, but a much larger number of coatings may be used, in some cases as many as eleven. In general the greater the decorative effect that is desired the larger is the number of coatings that is needed.
Representative patents of the prior art include U.S. Pat. Nos. 3,708,320; 3,600,256; 3,666,516; 3,949,139; 3,770,478; 3,770,479; 3,940,864; 4,053,672; 4,084,032; 4,007,067; and 4,047,996.
The prior art transfer laminates for heat transfer films require a significant number of separate layers, typically a separate layer for each of the various functions associated with the laminate. When the transfer film is used in creating a pictorial transfer, it is necessary to include pigment in a pattern. Since the transfer layer has to be releasable it is customary to include a coating that serves primarily a release function. The required inclusion of a large number of different layers in the laminate results in substantial cost and a significant use of materials.
Accordingly, it is an object of the invention to facilitate the production and use of hot transfer films and related heat transfer structures. Another object is to reduce the required number of layers in the laminate needed to accomplish a prescribed set of functions in heat transfer films. A related object is to reduce the cost of producing suitable heat transfer films. Another related object is to reduce the amount of materials required for heat transfer films.
The most common employment of heat transfer films is for making decorative and coding imprintings. The latter consists of a set of alpha numeric characters which carry information about the product that has been imprinted.
Accordingly, it is still another object of the invention to facilitate the imprinting of objects. A related object is to facilitate the coded imprinting of objects.
Heat transfer films are commonly used in the imprinting of hard surfaces, for example, those associated with thermoplastic materials where conventional printing techniques can produce smudging or smear. Heat transfer films are also employed for the imprinting of resilient, non-porous and non-retentive surfaces. They are used to advantage with irregular surfaces where conventional imprints are unsatisfactory.
Accordingly, it is yet another object of the invention to facilitate the imprinting of non-porous, non-retentive and irregular surfaces. A related object is to improve the efficiency with which heat transfer films can be used in the imprinting of resilient, porous, non-retentive and irregular surfaces.
Another important use for heat transfer films is in the decoration of multi-dimensional objects. When conventional inks are used in this situation it is necessary to permit each imprinted surface to dry before any further imprint can be made. In general the conventional imprinting of multi-dimensional surfaces results in characters that tend to be blurred and lack sharpness. Thermal imprints permit high speed operation since there is no need for drying.
Accordingly, it is yet another object of the invention to increase the rate at which multi-dimensional objects can be imprinted. It is another object to achieve increased sharpness of character imprint. Still another object is to enhance the efficiency with which multi-dimensional imprinting can be achieved with heat transfer foils.